Moves maintaining ShellObservers back to Shell

components/exo/wm_helper_ash.cc

Index: components/exo/wm_helper_ash.cc
diff --git a/components/exo/wm_helper_ash.cc b/components/exo/wm_helper_ash.cc
index 413eeb8e6a60302aea0b24eba02c7a5bdcc878e1..23398362955cec17a60e63f89a91c9ab5445e1e5 100644
--- a/components/exo/wm_helper_ash.cc
+++ b/components/exo/wm_helper_ash.cc
@@ -21,7 +21,7 @@ namespace exo {
 // WMHelperAsh, public:
 
 WMHelperAsh::WMHelperAsh() {
-  ash::WmShell::Get()->AddShellObserver(this);
+  ash::Shell::GetInstance()->AddShellObserver(this);
   ash::Shell::GetInstance()->activation_client()->AddObserver(this);
   aura::client::FocusClient* focus_client =
       aura::client::GetFocusClient(ash::Shell::GetPrimaryRootWindow());
@@ -37,7 +37,7 @@ WMHelperAsh::~WMHelperAsh() {
       aura::client::GetFocusClient(ash::Shell::GetPrimaryRootWindow());
   focus_client->RemoveObserver(this);
   ash::Shell::GetInstance()->activation_client()->RemoveObserver(this);
-  ash::WmShell::Get()->RemoveShellObserver(this);
+  ash::Shell::GetInstance()->RemoveShellObserver(this);
   ui::DeviceDataManager::GetInstance()->RemoveObserver(this);
   ash::WmShell::Get()->system_tray_notifier()->RemoveAccessibilityObserver(
       this);